There have been known image projection devices such as head-mounted displays (HMDs) that directly project an image onto the retina of the user by using a light beam emitted from a light source (for example, Patent Document 1). Such image projection devices employ a method called Maxwellian view. In Maxwellian view, the light beam forming an image is made to be converged on the vicinity of the pupil to project the image onto the retina.
There has been also known an image projection device that scrolls an image or turns a page in accordance with the direction of movement of the eyeball of the user and recognizes the movement speed of the eyeball of the user to determine the scrolling increment in accordance with the recognized speed (for example, Patent Document 2). There has been also known an image projection device that relates the speed of the visual line during saccadic movement of the eye of the user to the degree of asthenopia, and changes a warning message depending on the degree of asthenopia (for example, Patent Document 3).